This invention relates to a shock absorber for absorbing a shock of a moving member, such as work, in case the moving member is transferred from a moving state to a stopping state.
A conventional shock absorber includes a cylinder, a bearing fixed to the cylinder such that a center of the bearing is located on a center line of the cylinder, and a piston moving in the cylinder and having a shaft. The piston slides along the bearing pushed by moving member. The shock absorber is structured such that when a forward end of the piston pushed by the moving member approaches an inner end of the cylinder, compressed oil is circulated to a back side of the piston through an orifice provided to, for example, the piston or cylinder, to thereby absorb a shock of the moving member.
Then, in case the moving member is retracted and the pressing force applied to the piston is removed, the piston is restored to an original position by a force of a restoring spring incorporated in the shock absorber or attached to an outside thereof.
In the above conventional shock absorber, as the forward end of the piston approaches the inner end of the cylinder, a reactive force of the restoring spring becomes strong in addition to a resistance force caused by compressed oil circulating in the orifice to thereby suddenly increase the whole reactive force. Therefore, the forward end of the piston pushed by the moving member may not reach a stopping surface of the cylinder, i.e. may not completely contact the stopping surface.
Further, a fatigue and creep relaxation occur to the restoring spring with the lapse of time, which results in a defective product.
Also, in the conventional shock absorber, in case there is required a signal to be outputted to a controlling device of the moving member when the forward end of the piston pushed by the moving member reaches the stopping surface of the cylinder, in other words, if the contact signal is required, a user has to provide a switching device for detecting a movement of the moving member or a movement of the piston shaft, separately.
In view of the above defects, the present invention has been made, and an object of the invention is to provide a shock absorber, wherein a restoring spring is omitted by restoring a piston by an air force without a signal from an outside, and at the same time, in order to allow the piston to firmly contact, when a forward end of the piston pressed by a moving member reaches an inner end of the cylinder, a compressed air in the inner portion of the cylinder is ejected.
Another object of the invention is to provide a shock absorber as stated above, wherein a contact signal indicating a contact of the piston to the inner end of the cylinder is outputted to a controlling circuit of the moving member.
Further objects and advantages of the invention will be apparent from the following description of the invention.